This invention generally relates to air bearing surfaces on sliders used with magnetic recording heads in a magnetic disk drive assembly. More particularly, this invention relates to modifying the air bearing surface at the trailing edge of the slider to reduce the pressure gradients created by the air flow, the air bearing surface and the spinning disk beneath it.
Head assemblies in hard disk drives include a magnetic transducer to write data onto a disk and/or read data previously stored on a disk. A thin film transducer performs both read and write operations. A magneto-resistive transducer performs only read functions and must be used in combination with a thin film transducer for full read/write capabilities. Regardless of the magnetic transducer employed, head assemblies typically include a body or slider having an air bearing surface which, in part, functions to position the magnetic transducer a specified distance from the surface of the disk. Air bearing surfaces vary, but generally include one or more elongated sections called rails that may extend substantially the length of the slider, but typically less than the width. The rails may or may not be connected to each other at various sections. The magnetic transducer typically is positioned towards the trailing edge of the air bearing surface.
A primary goal of disk drive assemblies is to provide maximum recording density on the disk. A related goal is to increase reading efficiency or to reduce reading errors, while increasing recording density. Reducing the distance between the magnetic transducer and the recording medium of the disk generally advances both of those goals. Indeed, from a recording standpoint, the slider is ideally maintained in direct contact with the recording medium (the disk) to position the magnetic transducer as close to the magnetized portion of the disk as possible. However, since the disk rotates many thousands of revolutions per minute or more, continuous direct contact between the slider and the recording medium can cause unacceptable wear on these components. Excessive wear on the recording medium can result in the loss of data, among other things. Excessive wear on the slider can result in contact between the magnetic transducer and recording medium resulting, in turn, in failure of the magnetic transducer, which can cause catastrophic failure.
Similar to recording, the efficiency of reading data from a disk increases as the read element is moved closer to the disk. Because the signal to noise ratio increases with decreasing distance between the magnetic transducer and the disk, moving the magnetic transducer closer to the disk increases reading efficiency. As such, magneto-resistive heads in current disk drives typically operate at an average spacing from the disk surface of approximately 30 nanometers to up to approximately 70 This range of spacing is required due to several reasons, including manufacturing tolerances of the components, texturing of the disk surface and environmental conditions, such as altitude and temperature. These factors, and others, result in variances in the spacing between the magnetic transducer and the disk, which can cause the magnetic head to fly too low and contact the spinning disk.
To prevent undue wear of the magnetic transducer and the recording medium while maintaining an acceptable recording density, the bottom surface of sliders typically are configured as an air bearing surface. The rotation of the disk creates a flow of air along its surface. The air bearing surface interacts with the air flow, causing the slider to float above the spinning disk surface. As long as the disk is spinning and the slider is positioned above the disk, the slider floats slightly above the disk, thereby substantially eliminating wear to both the disk and the slider. This behavior is characterized by the Reynold""s equation.
When the assembly is at rest, the bottom surface of the slider generally rests directly on the surface of the disk. When the assembly is in operation, the moving air generated by the spinning disk lifts the slider off the surface of the disk and opens a volume of space through which air flows. As the slider lifts off the surface of the disk, it typically is positioned at an angle relative to the disk, with the trailing edge closest to the surface of the disk. Because the air bearing surface is on the bottom of the slider and has a generally flat surface parallel to the slider and because the slider is free to pivot, the trailing edge of the air bearing surface is closer to the surface of the disk than is the leading edge of the air bearing surface. As air flows through this space, from the leading edge to the trailing edge of the slider, the pressure of the air builds as the air passes through a diminishing volume of space. The pressure typically reaches a maximum near the trailing edge of the slider, where the distance between the slider and the disk approaches its minimum. Beyond the boundary of the trailing edge of the slider, the compressed air returns to atmospheric pressure, creating a pressure gradient. Other pressure gradients may also be created along the other edges of the slider.
One type of slider design utilizes two separate rails running essentially the length of the slider. This design, referred to as an open design, is relatively slow to lift the head assembly off the disk. To attempt to overcome this, another type of slider design utilizes two rails joined at the leading edge to form, from the bottom view, a U-shaped configuration. This U-shaped slider design, also referred to as a closed design, allows for the formation of sub-ambient pressure under the slider, which in turn allows for the generation of more positive pressure to more quickly lift the assembly head off the disk.
In existing slider designs, a significant pressure gradient can result in the formation of liquid droplets on the slider, if condensable vapors, such as water vapor, are present in the air between the slider and the disk. The accumulation of such liquid can cause severe problems. For example, after the disk stops spinning, the slider rests in static contact with the surface of the disk. The liquid formed on the slider may cause the slider to adhere to the surface of the disk, inhibiting or even preventing the slider from separating from the disk in subsequent operation. This adhesive force can be sufficient to cause the entire magnetic disk drive assembly to fail.
Therefore, a need exists to reduce pressure gradients, and the resulting liquid droplet formations, that are caused by the structure and operation of existing magnetic disk drive assemblies.
The present invention generally relates to improvements in the design and operation of air bearing surfaces on sliders used with head assemblies in a magnetic disk drive. More particularly, in one embodiment of the present invention, the air bearing surface of a slider has a recess adjacent the trailing edge to reduce the pressure gradient created by the air flow passing between the spinning disk and the trailing edge of the slider and reduce the formation of liquid droplets on the slider. This recess may take any of several forms, including one or more steps, an inclined plane or even a curve.
In another embodiment of the invention, the rail on which the air bearing surface is formed has a leading surface with a defined height and a trailing surface with a defined height less than that of the leading surface. The difference in these heights reduces the pressure gradient created by the air flow of an operating assembly and reduces the formation of liquid droplets.
In yet another embodiment of the invention, the rail on which the air bearing surface is formed has a leading surface with a height greater than the height of the trailing surface, and a bottom surface with a first section that is substantially planar from the leading surface almost to the trailing surface and a second section that extends from the end of the first section to the trailing surface. The bottom surface of this second section may be of several forms, including one or more steps, an inclined plane or even a curve.
In another embodiment of the invention, the difference between the height of the leading edge of a rail and the height of the trailing edge of a rail may be proportional to or may be substantially the same as the flying height of the slider.
In another embodiment of the invention, other portions of the air bearing surface of a slider are modified to reduce the pressure buildup and/or the pressure gradients resulting from the air flow over the spinning disk.
The invention is further embodied in a method to reduce the formation of pressure gradients associated with a magnetic disk drive assembly by generating a flow of air between a recording medium and the assembly, positioning the assembly within a predetermined range of distances from the recording medium, allowing the flow of air to create pressure therein and releasing at least a part of the pressure through a recess near the trailing edge of the assembly.